1. Field of the Invention
The present invention relates to a lens barrel capable of zoom operation, and relates to an image pickup apparatus such as a digital camera having the lens barrel.
2. Description of the Related Art
Some conventional zoom lens barrel includes a fixed cylinder having an inner peripheral surface thereof formed with cam grooves, a cam cylinder having cam pins for engagement with the cam grooves of the fixed cylinder, and a lens retainer having cam pins for engagement with cam grooves formed on an inner peripheral surface of the cam cylinder. The cam cylinder moves along an optical axis direction while rotating. With rotation of the cam cylinder, the lens retainer relatively moves in the optical axis direction for zooming and retracting operations.
With recent trend that image pickup apparatuses are made smaller in thickness and higher in magnification, the zoom lens barrel of the above construction has rectilinear guide grooves for causing the lens retainer to rectilinearly move in the optical axis direction. The rectilinear guide grooves are formed on the inner peripheral surface of the fixed cylinder so as to extend across and divide the cam grooves formed on the fixed cylinder.
However, the rectilinear guide grooves formed in this manner cause a fear that the cam pins of the lens retainer are disengaged from the cam grooves of the fixed cylinder at positions where the cam grooves are divided by the rectilinear guide grooves, or that the cam pins or the cam grooves are worn.
Thus, a zoom lens barrel has been proposed in which first and second cam grooves used in respective ones of a photographing region and a non-photographing region are formed on the inner peripheral surface of the fixed cylinder and in which first and second cam pins for engagement with respective ones of the first and second cam grooves are formed on the outer peripheral surface of the cam cylinder (Japanese Laid-open Patent Publication No. 2006-220898).
This proposal contemplates to smoothly drive the zoom lens barrel by engaging the second cam pins with the second cam grooves not divided by the rectilinear guide grooves when the first cam pins are at positions where the first cam grooves are divided by the rectilinear guide grooves.
However, this lens barrel causes a fear that the cam pins are caught in cam groove entrances at the time of switching between the retracted region and the photographing region so that the zoom operation is adversely affected. In addition, a relatively large driving load is applied to the lens barrel at the time of barrel retraction and at the time of photographing since the cam pins are in engagement with the cam grooves both in the retracted region and in the photographing region.